Electrically conducting polymers

ABSTRACT

An electrically conducting organic material for use on battery electrodes and the like, which comprises a polymer optionally doped with an n- or p-type dopant, wherein the polymer contains along its backbone at least one π-conjugated linear unit of formula (i), wherein A is a divalent optionally-substituted conjugated organic cyclic group containing a π-conjugated sequence of single bonds and at least two double bonds; B is a tetravalent optionally-substituted conjugated organic cyclic group containing a π-conjugated sequence of single bonds and at least one double bond; A and B have the same molecular and structural formula except that they contain a different configuration of double and single bonds; Y is a trivalent group containing m linking atoms between adjacent groups A and B where m is an odd number from 1 to 11, provided that when Y contains more than one linking atom between said adjacent groups, the linking atoms form a π-conjugated chain of atoms between said adjacent groups A and B, and n is an integer from 1 to 4. One example of the material is poly(2,2&#39;-dipyrrylmethane) doped with CF 3  SO 3  ions, which is relatively air-and water-stable and has a conductivity of about 1.0S cm -1 .

This invention relates to electrically conducting polymers, to films ofthese polymers on electrodes, and to processes for preparing thesepolymers.

For several years it has been known that organic polymers containing aπ-conjugated backbone structure have desirable electrical conductivitiesfor a range of applications. These applications include coatings onelectrodes for batteries, galvanic cells, and electrochromic displaydevices. Probably the best known of these polymers is polyacetylene,especially trans-polyacetylene. These polymers may be doped withconductivity increasing amounts of an electron acceptor (p-type) dopantand/or a conductivity-decreasing amount of an electron donor (n-type)dopant to produce families of polymeric materials whose conductivitiesrange from semiconductor behaviour to metallic behaviour. Methods ofdoping these polymers with n- and/or p-type dopants are disclosed inU.S. Pat. Nos. 4,204,216, 4,222,903, and 4,321,114. Polyphenylene isanother conducting polymer disclosed in these patents.

More recently, a series of heterocyclic monomer-based homopolymers havebeen developed which, to a certain extent, overcome some of the maindisadvantages of polyacetylene that include environmental instabilityand instability in the presence of electrolytes and dopant ions. Theseinclude polypyrrole which has been used in electrochromic displaydevices (Inganas and Lundstrom, J Electrochem Soc (1984) 131(5),1129-1132 and U.S. Pat. No. 4,304,465). However, it is reported byInganas and Lundstrom that polypyrrole is readily attacked by oxygen andelectrolytes, necessitating ring substitution on the N heteratom whichis not always desirable for other reasons. Similar ring substitution isdisclosed in EP-A-No. 0095973 which discloses polymers of pyrrole,thiophene and furan that are substituted in the 3 and/or 4 ringpositions with groups such as alkyl, cyano and halo. These polymers aredisclosed as useful in batteries.

BRIEF DESCRIPTION OF DRAWING

Accompanying FIG. 1 is a graphical representation of the polymerisationpotential against polymerisation time characteristics for theelectrochemical polymerisation of 2,2'-dipyrrylmethane described inExample 1.

It is one object of the present invention to provide an alternative,novel conducting polymer which in some instances provides an alternativeto ring substitution for stabilising cyclic monomer-based conductingpolymers.

According to a first aspect of the present invention there is providedan electrically conducting organic material which comprises a polymeroptionally doped with an n- or p-type dopant, wherein the polymercontains along its backbone at least one π-conjugated linear unit offormula I ##STR1## wherein A is a divalent optionally-substitutedconjugated organic cyclic group containing a π-conjugated sequence ofsingle bonds and at least two double bonds;

B is a tetravalent optionally-substituted conjugated organic cyclicgroup containing a π-conjugated sequence of single bonds and at leastone double bond;

A and B have the same molecular and structural formula except that theycontain a different configuration of double and single bonds;

Y is a trivalent group containing m linking atoms between adjacentgroups A and B where m is an odd number from 1 to 11, provided that whenY contains more that one linking atom between said adjacent groups, thelinking atoms form a π-conjugated chain of atoms between said adjacentgroups A and B, and n is an integer from 1 to 4. The polymer willnormally be copolymer of the groups A, B and Y and contain severalrepeat units of Formula I.

A and B are preferably independently selected fromoptionally-substituted homocyclic groups containing less than 7 ringatoms and optionally-substituted heterocyclic groups containing lessthan 7 ring atoms. As an example of a suitable homocyclic group, A maybe an optionally-substituted p-phenylene group and B a correspondingoptionally-substituted 1,4 cyclohexadiene group of formula ##STR2## Morepreferably, however, the linear unit is of general formula II ##STR3##wherein X is a Group VIa atom or an optionally-substituted Group Vaatom, and R¹ and R², when taken separately, are the same or differentand each is selected from the group consisting of H,optionally-substituted alkyl, optionally-substituted alkoxyl,optionally-substituted aryl, optionally-substituted amino, halo andcyano or, when taken together, are optionally-substituted benzo. X ispreferably NR, S or O where R is H, optionally substituted aryl, oroptionally-substituted alkyl. Where any one of R, R₁ ¹ and R² consistsof or contains an optionally-substituted alkyl group, the alkyl group ispreferably a C₁ -C₅, especially an nC₁ -C₅, alkyl group. Mostpreferably, X is NH or S and R¹ and R² are both H.

The group Y in general formula I given above is preferably (CR³)_(2x-1)in which R³ is H or an optionally substituted alkyl, especially a C₁ -C₅alkyl, group and x is an integer from 1 to 6. Most preferably, Y is CH.n is preferably 2 or 4, and is most preferably 2.

The polymer is preferably doped with either n-type (electron doning)cationic dopant ions, or, more preferably, with p-type (electronwithdrawing) anionic dopant ions. Suitable dopants ions and methods ofincorporating these ions into the polymer are disclosed in U.S. Pat. No.4,321,114 (Heeger et al). A wide variety of dopant species may suitablybe employed, either individually or in combination, for effectivelymodifying the room temperature electrical conductivity of the conjugatedpolymer in accordance with the present invention.

Suitable anionic dopant ions for effecting p-type doping include, forexample, I⁻, Br⁻, Cl⁻, F⁻, ClO₄ ⁻, AlCl₄, PF₆ ⁻, AsF₆ ⁻, AsF₄ ⁻, SO₃ CF₃⁻, BF₄ ⁻, BCl₄ ⁻, NO₃ ⁻, POF₄ ⁻, CN⁻, SiF₃ ⁻, CH₃ CO₂ ⁻ (acetate), C₆ H₅CO₂ ⁻ (benzoate), CH₃ C₆ H₄ SO₃ ⁻ (tosylate), SiF₆ ⁻⁻, SO₄ ⁻⁻, or thelike.

The cationic dopant ions suitable for effecting n-type doping arecations of a metal whose Pauling electronegativity value is no greaterthan 1.6. A complete list of such metals and their correspondingelectronegativity values are provided in Table I below.

                  TABLE I                                                         ______________________________________                                        Metal      Electronegativity Value                                            ______________________________________                                        Cs         0.7                                                                Rb         0.8                                                                K          0.8                                                                Na         0.9                                                                Ba         0.9                                                                Li         1.0                                                                Sr         1.0                                                                Ca         1.0                                                                Mg         1.2                                                                Y          1.3                                                                Sc         1.3                                                                Be         1.5                                                                Al         1.5                                                                Zr         1.6                                                                Ti         1.6                                                                ______________________________________                                    

The above list of metals includes all of the alkali metals, all of thealkaline earth metals, and certain of the metals from Group 3 (Y, Sc andAl) and Group 4 (Zr and Ti) of the Periodic Table.

Other cations which could be used include Fe²⁺, Fe³⁺, and R₄ ^(a) N⁺where R^(a) is a C₁ -C₅ alkyl group.

Each of the anionic and cationic dopant ion species set forth above willeffect an increase, to varying degrees, in the room temperatureelectrical conductivity of the starting conjugated polymer. For thewidest range in selectivity as to achievable conductivities, thepreferred cationic dopant ions are alkali metal ions, particularly Li⁺ ;and the preferred anionic dopant ions are halide ions, ClO₄ ⁻, PF₆ ⁻,AsF₆ ⁻, AsF₄ ⁻, SO₃ CF₃ ⁻, and BF₄ ⁻.

The molar ratio of cyclic groups in the polymer to dopant ions in thematerial preferably lies in the range 1:0.01 to 1:5.

The present polymers containing units of formula II may be prepared bythe oxidation of precursor polymers having repeat units

    --A).sub.n (Y)H]

where A and Y are as defined above, to generate the required sequence ofdouble bonds. Preferably, however, these particular polymers areprepared by chemical- or electro-oxidative polymerisation. Where n is 1,it is preferred that the polymer is prepared by the chemical oxidativeco-polymerisation of monomeric precursors for example by condensationpolymerisation followed by oxidation. Where n is 2, then the polymersare preferably prepared by first preparing a precursor monomer offormula HA-(Y)H-AH (eg 2,2'-dipyrryl methane), and thenelectro-oxidatively polymerising the monomer. The polymeric product isconveniently filmed onto the anode of a cell from a solution of themonomer conveniently containing a salt to improve the ionic conductivityof the solution. The advantage of electro-oxidative polymerisation isthat the product polymer is filmed onto an electrode ready for use in,for example, a battery. Furthermore, the salt in the solution willprovide a source of dopant ions that will dope the polymer during itsformation and so generally improve its conductivity.

According to a second aspect of the present invention, therefore, thereis provided an electrode for use in a galvanic cell, a battery, anelectrochromic display device or an optical storage device, which hasthereon a film of an electrically conducting organic material accordingto the first aspect. The thickness of the film is preferably from 0.01microns to 2 mm, most preferably from 0.05 microns to 100 microns,depending on the use to which the electrode is to be put.

According to a third aspect of the present invention there is provided aprocess of depositing an electrically conducting organic material onto asubstrate, which comprises electrochemically oxidising, between an anodeand a cathode, a monomer of general formula III

    H(A).sub.p [Y.sup.1 H--A).sub.p ].sub.q H                  III

dissolved within a solvent, wherein

A is a divalent optionally-substituted conjugated organic cyclic groupcontaining a π-conjugated sequence of single bonds and at least twodouble bonds, and is preferably a hetero- or homo-cyclic groupcontaining less than 7 ring atoms,

Y¹ is CR³ in which R³ is an optionally-substituted C₁ -C₅ alkyl group,

p is 1 or 2, and

q is an integer from 1 to 3,

whereby the film is deposited onto the anode.

In general formula III, Y¹ is preferably CH, p is preferably 1, and q ispreferably 1.

A is preferably ##STR4## wherein X is a Group VIa atom or anoptionally-substituted Group Va atom, and R¹ and R², when takenseparately, are the same or different and each is selected from thegroup consisting of H, optionally-substituted alkyl,optionally-substituted alkoxyl, optionally-substituted aryl, optionallysubstituted amino, halo and cyano or, when taken together, areoptionally-substituted benzo. X is preferably NR, S or O where R is H,optionally substituted aryl, or optionally-substituted alkyl. Where anyone of R, R₁ ¹ and R² consists of or contains an optionally-substitutedalkyl group, the alkyl group is preferably a C₁ -C₅, especially an nC₁-C₅, alkyl group. Most preferably, X is NH or S and R¹ and R² are bothH.

Preferred monomers of general Formula III are 2,2' dipyrrylmethane and2,2' dithienylmethane.

The material is usually deposited as a film. The solvent preferablycontains an electrolyte compound that is ionisable in the solvent toprovide anionic dopant ions that dope the depositing material aselectrochemical oxidation proceeds. The presence of the compound speedsup film deposition and will generally improve the conductivity of theresultant polymeric material. Suitable anionic dopant ions include anyone of those listed as suitable for inclusion in the material accordingto the first aspect of the present invention.

One use of the materials according to the first aspect of the presentinvention, and, more especially, of the polymeric product of the processaccording to the third aspect of the present invention, is in batteriesand the like.

Conventional battery systems such as the nickel-cadmium or lead-acidtypes suffer from the problem of low energy densities. Alternativelithium anode based batteries have much improved theoretical energydensities and high values are achieved in practicable cell arrangementssuch as by using the lithium/thionyl chloride and lithium/sulphurdioxide couples. Excellent power densities and open circuit potentialsare common although the safety aspects of such systems could be improvedby using alternative electrode and electrolyte arrangements. However thechemical reversibility of such lithium cells is usually quite limited.One approach to improve the situation for the cathode has been to uselithium ion intercalants such as titanium disulphide. Another variety ofmaterial for possible electrode application includes electricallyconducting polymers having extended π-conjugation sequences, the mostwell known example being polyacetylene; they may be used either asanodes or cathodes if a suitable doping process is possible. Again fullchemical reversibility over many charge-discharge cycles is desired,however results show that for polyacetylene high coulombic efficienciesare obtained only if the material is not oxidised beyond a 6 mole %limit.

Thus the present polymeric material may be used in a galvanic cell, aphotogalvanic cell, or a battery comprising an anode, a cathode and anelectrolyte contained between the electrodes, wherein one or both of theactive components of the electrodes comprises in part or in whole amaterial according to the first aspect of the present invention or, mostpreferably, the polymeric product of the process according to the thirdaspect of the present invention. It is important that the polymer filmbe adherent to the backing electrode and form good electrical contact.The thickness of the polymeric film formed would be controlled by thetotal amount of charge passed during the polymerisation. The desiredthickness of film grown would be dependent on the requiredcharacteristics for the cell. A greater mass of polymer could becompatible with a cell of high capacity but would possibly give a lowercurrent drain rate and power density under commensurate conditions asfor a thinner-film electrode device. Depending on the geometry of thecell or battery site available, it is preferred that the electrode filmsbe relatively thin, less than 50 μm and preferably less than 25 μm butthicker than 0.01 μm. Alternatively procedures for forming a film of theelectrode material include casting or spin-casting from a solution ofthe polymer in a suitable solvent. Secondly the polymer may be depositedas an insoluble film from the polymerisation reaction.

All the cells or batteries described herein may be used in either aprimary or secondary mode. The number of discharge-charge cycles, andamount of charge, as a fraction the total practicable capacity of thebattery, in a typical cycle, which will be attainable will be dependenton the construction, materials and morphologies of said materials in thebatteries made. However this invention is not limited or constrained bythis.

The principal advantages of the polymeric materials described in thisinvention, over other electronically conducting polymers, are improvedstability in a variety of environments and doping states, particularlyhigh mole % doping levels. Stability to doping, most particularlyp-doping of the polymers described in this invention, when in contactwith aqueous electrolytes, is an advantage of the polymeric materials ofthis invention.

The polymeric electrode chosen from the types given in this inventionmay be synthesised and fabricated by conventional techniques. It ispreferred that the process may be combined into a single operation, forexample the monomer may undergo an electrochemically driven orphotoelectrochemically driven, by appropriate choice of a semiconductorelectrode, an oxidative coupling reaction to given a film of the desiredpolymer or an intermediate or precursor polymer. Alternatively if thepolymeric electrode material is soluble in a suitable solvent, thenfilm-formation may be achieved by solvent evaporation. If the polymer isinsoluble then the synthetic procedure would be designed such that thewanted polymer is formed as a thin film covering the region allotted forthe electrode. The performance of the reulting electrode may be verydependent on the nature of the morphology created. Ways of controllingthis aspect using the above electrochemical synthetic route include:variation of the monomer concentration, the current density, appliedpotential, the material and makeup of the electrode and the electrolytesolvent ans salt. If the polymer is prepared by a conventional syntheticroute or other route apart from electro-oxidation then it may bedesirable to blend the electrically conducting polymer with thepolymeric electrolyte if this is appropriate in order to improvemechanical and physical properties and ion transport within the body ofthe electrode material. Where the polymeric electrode is formed in situin the presence of a polymeric electrolyte then this improvement ofmorphology and inter-phase contact may be expected to take place.

The method of fabrication of the cell may be achieved by conventionaltechniques however a most important aspect of the use of the materialsdescribed here is their ability to form thin coherent films so thatcontact areas are very high and consequently the necessary currentdensities may be small.

A further use of the materials according to the first aspect of thepresent invention and, more especially, of the polymeric product of theprocess according to the third aspect of the present invention, is inelectrochromic display devices and in optical storage (memory) devices.An electro-chromic display is a device wherein the display effect isachieved as a consequence of a redox reaction cause by the passage ofcharge between a display electrode and a counter electrode, bothcontacted by a suitable electrolyte. Examples of conventional displaysinclude those given in British Pat. No. 1,376,799 wherein a materialundergoing the redox reaction is heptyl viologen dication. Upon passageof charge, there is reduction of the viologen and a purple film isdeposited at the indicating or display electrode. On oxidation thedisplay is erased and the viologen returns to the electrolyte. Byproviding a plurality of display electrodes the required completedisplay can be constructed. Other organic materials employed includepolypyrrole and polythiophene or derivatives such aspoly(3-methylthiophene) as described in U.S. Pat. No. 4,304,465; FrenchPat. No. 2,527,843 and European Pat. No. 0095973.

In display and memory devices, the polymer property made use of is achange in the absorption spectrum of the polymer film in contact with abacking electrode and surrounded by an electrolyte when the content ofdoping or oxidation state of the polymer is changed. This is normallyachieved by changing the potential of the backing electrode. Thus thefilm may be switched between two or more levels of oxidation in order tochange the nature of the display or the content of the memory. When useda memory device, the oxidation state of the film is read optically bypassage of a beam of light of appropriate wavelength, not necessarilycorresponding to the visible region of the electromagnetic spectrum,over the film with a reflection arrangement or through the film with atransmission arrangement. Alternatively the memory may be readelectrically in which case the memory effect may be erased concurrentlywith the reading stage, though not necessarily so. A further method ofwriting the memory is to have the backing electrode as an appropriatesemiconductor electrode, such that when illuminated by light (thewriting step) of energy greater than the band gap between the valenceand conduction bands of the semi-conductor then the polymeric film wouldbe caused to change oxidation state. In order that a high density ofinformation storage can be achieved either known photolithographictechniques and integrated circuit methods may be used, or alternativelytechniques described in U.S. Pat. No. 4,427,513 may be utilised, for thedevelopment of desired patterns or arrays of displays or memoryelectrodes.

The term contrast is defined here as the difference in absorption orabsorbance, or reflection or reflectance, for a particular wavelength oflight, of the polymeric film in the two oxidation states considered.

The area of application of pyrrole based polymers for display and memorydevices is discussed in the paper by O Inganas and I Lunstrom, JElectrochemical Society, 1984, 131, 1129-1132 and the types of devicediscussed and important parameters relevant to the operation of suchdevices may be considered also relevant to the polymers of thisinvention.

The polymeric film may be doped with any of the n- or p-type dopantsthat are described above as suitable for doping the material accordingto the first aspect of the present invention.

The thickness of the polymeric film covering the backing electrode ispreferably from 0.01 to 5 microns and is most preferably from 0.05 to 1microns. For the property of a desired fast switching speed between thedesignated oxidation states of the polymer, it is advantageous to have athin polymeric film. For the property of a high contrast between thedesignated oxidation states of the polymer it may be advantageous tohave a relatively thick film, thus there is a compromise between thedesired properties and an optimum film thickness for a particularexample of polymer would be chosen.

The fabrication of individual displays and arrays of such may beaccomplished using known technologies. The final design would bedependent on the individual application. Possible uses are for displaysin watches and hand calculators. Different techniques would be appliedto develop high density memory storage units and the methods used mayresemble those described in U.S. Pat. No. 4,427,513.

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying FIG. 1, which is agraphical representation of the polymerisation potential againstpolymerisation time characteristics for the electrochemicalpolymerisation of 2,2'-dipyrrylmethane described in Example 1.

MATERIALS 1. Preparation of 2,2'-dipyrrylmethane (IV) ##STR5##

There are several known routes to the preparation of the monomer2,2'-dipyrrylmethane (IV). The method used here is outlined below.Firstly the corresponding ketone was made using the reaction procedureoutlined below: ##STR6##

A Grignard reagent was prepared in diethyl ether by a standard methodand distilled pyrrole was added to the resulting solution. After a 2hour reflux the solution produced was added at room temperature to asolution of phosgene in toluene and reaction allowed to occur over a 16hour period. Work-up of the reaction mixture gave the required product;the full method is described by A W Johnson and W R Overend, J C SPerkin I, 1972, 2681.

The second stage of the synthesis was the reduction of (V) by sodiumborohydride as described by R Chong, P S Clezy and A J Leipa, Austral. JChem 1969, 22, 229. The product was a solid (colourless needles) and hadthe required analytical properties. The material was stored in the darkunder vacuum prior to use.

2. Preparation of 2,2'-dithienylmethane (VII)

0.45 mol of about 40% w/v formalin solution was added to 0.4 mol ZnCl₂and 0.6 mol thiophene in 41 cm³ HCl (specific gravity, 1.0) at -7° C.,and the reaction mixture was stirred for 2 hours at -7° C. Water (80cm³) was then added and the reaction contents extracted with diethylether. The extracts were washed successively with water and sodiumbicarbonate and dried over anhydrous calcium chloride. On removal of thesolvent the product was vacuum distilled at 1.33 KPa. The majority (ca.25 g) of (VII) was collected at 130°-135° C. The final product obtainedafter redistillation was recrystallised from ethanol/pet.ether.

The full method is described by Y. L. Goldfarb and Y. L. Danyushevski,Bull. Acad. of Sci. USSR, Div. Chem. Sci., 1956, 1395.

SPECIFIC EXAMPLES Example 1 Electro-oxidative polymerisation of2,2'-dipyrrylmethane (IV)

Polymerisation was performed in a single major compartment, 3-electrodecell of total volume ca. 20 cm³, with the counter-electrode separatedfrom the remaining solution by a glass sinter. An oxygen-free nitrogenatmosphere was maintained within the cell and whole arrangement wastemperature controlled. The electrolyte employed was vacuum driedpoly(ethylene glycol) of average molar mass 200 containing lithiumtrifluoromethanesulphonate (0.1 mol dm⁻³) and 0.1 mol dm⁻³2,2'-dipyrrylmethane, maintained at 52° C. The anode was either aplatinum flag or a tin oxide transparent conducting glass with a counterelectrode of aluminium and calomel reference electrode. Duringpolymerisation a constant current of 50 μA cm⁻² was passed at the anodefor periods of 30 to 240 minutes depending on the film thicknessrequired. Electrode deposited films had a metallic green-blackappearance. The potential-polymerisation time characteristic is given inthe graph illustrated in FIG. 1. The thickness of the film after 240minutes was about 1 mm. Thinner films were also produced using shorterreaction times. The films produced were ethanol washed and dried undervacuum.

The films were found to be flexible and showed a conductivity, measuredby a standard 4-point-probe method, of about 1 S cm⁻¹ at roomtemperature.

The uv-visible spectrum of a thin film of the polymeric product, whichhad a metallic purple and slightly transparent appearance, did not varyover several days after exposure of the film to a laboratory atmosphere,demonstrating its environmental stability.

Elemental analysis (C,H,N) indicated that the polymer to salt ratio inthe doped films was ca. 2.4:1 ie (C₉ H₇ N₂)₂.4 CF₃ SO₃.

The overall combined electrosynthesis and doping procedure may besummerised by the equation: ##STR7##

Example 2 Oxidative polymerisation of 2,2'-dipyrrylmethane in aqueoussolution

The process used was an interfacial polymerisation where equal volumesof an aqueous 30% (w/v) iron (III) chloride solution and toluenecontaining 0.05 mol dm⁻³ 2,2'-dipyrrylmethane were allowed to react atroom temperature. After 2 hours, a thin metallic green-black polymericfilm was apparent at the interface between the organic and aqueousphases. After about 4 hours, the film was thick enough to be liftedintact from the reaction mixture. The retention if the film's colourindicated its stability in an aqueous environment.

Example 3 Synthesis and polymerisation of 2-bromomethylthiophene (VI)##STR8##

2-Bromomethylthiophene (VI) was made by the method of J. Braun, R.Fussganger and M. Kuhn, Annalen, 1925, 445, 201. The monomer wasobserved to darken and `self-polymerise`, particularly at elevated (>50°C.) temperatures, with the evolution of hydrogen bromide.

Pressed pellets formed from the powdery product, on doping with iodinevapour gave resultant 4-point-probe conductivities of only 2.5×10⁻⁵ Scm⁻¹. Thus only a partially conjugated system may have been generated orthe doping stage may have a low efficiency. However, the conductivitiesrecorded here are similar to those found for dopedpoly(N-methylpyrrole), ca 10⁻⁵ S cm⁻¹, though are lower than forpolypyrrole.

Example 4 Preparation of poly(pyrrole methine) (IX) ##STR9##

Poly(pyrrole methine) was prepared by the condensation reaction ofpyrrole with formaldehyde. Pyrrole and a formalin solution (about 40%w/v formaldehyde) in a pyrrole: formaldehyde molar ratio of about 1:1were reacted together at ambient temperature under an air atmosphere.The reaction time was varied between 30 minutes and 6 hours for severalreaction batches, after which the volalite components of the reactionmixture were removed. Typically, the product was deeply coloured orblack. The product varied from a low molar mass polymer (30 minutesreaction time) to a crosslinked brittle solid (6 hours reaction time).When the reaction was allowed to proceed to completion (6 hours reactiontime), the infra-red carbonyl absorption was no longer detectable in theproduct. The products were all found to be air and water stable.

Example 5 Electro-oxidative polymerisation of 2,2'-dithienylmethane(VII)

The process of Example 1 was repeated using 2,2'-dithienylmethane inplace of 2,2'-dipyrrylmethane. The temperature, time, and currentdensities employed during polymerisation were all the same as those usedin Example 1. A coherent and deeply coloured film was observed to formon the anode.

The combined reaction and doping step can be summarised by the followingequation: ##STR10##

Example 6

The monomer (VIII) was isolated by the method of Goldfarb et al (seepreparation of 2,2'-dithienylmethane described above) and waselectro-oxidatively polymerised using the method of Example 5. Thecombined reaction and doping step can be summarised by the followingequation: ##STR11##

I claim:
 1. An electronically conducting organic material comprising apolymer containing along its backbone at least one linear unit offormula I:wherein X is O, S or NR, where R may be H, aryl, substitutedaryl, alkyl or substituted alkyl; R¹ and R², when taken separately, arethe same or different and each is selected from the group consisting ofH, alkyl, substituted alkyl, alkoxyl, substituted alkoxyl, aryl,substituted aryl, amino, substituted amino, halo and cyano or, whentaken together, are benzo or substituted benzo; Y is (CR³)_(2x-1) inwhich R³ is selected from the group consisting of H, alkyl andsubstituted alkyl and x is an integer from 1 to 6; and n is an integerfrom 1 to
 4. 2. The electrically conducting organic material accordingto claim 1, wherein X is selected from the group consisting of NH and S,and R¹ and R² are both H.
 3. The electrically conducting organicmaterial according to claim 1, wherein n is
 2. 4. The electricallyconducting organic material according to claim 1, wherein Y is CH. 5.The electrically conducting organic material according to claim 1,wherein the polymer is additionally doped with n- or p-type dopant ions.6. The electrically conducting organic material according to claim 5,wherein the molar ratio of the cyclic groups in the polymer to dopantions in the material is within the range of 1:0.01 to 1:5.
 7. Anelectrode for use in a galvanic cell, a battery, an electrochromicdisplay device or an optical storage device, which has thereon a film ofan electrically conducting organic material which has a thickness offrom 0.01 microns to 2 mm and which comprises a polymer containing alongits backbone at least one linear unit of formula I: ##STR12## wherein Xis O, S or NR where R may be H, aryl, substituted substituted aryl,alkyl substituted alkyl,R¹ and R², when taken separately, are the sameor different and each is selected from the group consisting of H, alkyl,substituted alkyl, alkoxy, substituted alkoxyl, aryl, substituted aryl,amino, substituted amino, halo or cyano or, when taken together, arebenzo or substituted benzo; Y is (CR³)_(2x-1) in which R³ is selectedfrom the group consisting of H and substituted alkyl and x is an integerfrom 1 to 6; and n is an integer from 1 to
 4. 8. The electrode accordingto claim 7, wherein the film has a thickness of from 0.05 microns to 100microns.
 9. A process of depositing an electrically conducting organicmaterial onto a substrate, which comprises electromechanicallyoxidizing, between an anode and a cathode, a monomer of formula II:##STR13## wherein X is O, S or NR, where R is H, aryl, substituted aryl,alkyl or substituted alkyl R¹ and R², when taken separately, are thesame or different and each is selected from the group consisting of H,alkyl, substituted alkyl, alkoxyl, substituted alkoxyl, aryl,substituted aryl, amino, substituted amino, halo and cyano or, whentaken together, are benzo, optionally substituted banzo, R³ is hydrogen,a C₁ -C₅ alkyl group or a substituted C₁ -C₅ alkyl group, p is 1 or 2and q is an integer from 1 to 3, dissolved in a solvent, whereby thefilm is deposited onto the anode.
 10. The process according to claim 9,wherein R³ is hydrogen.
 11. The process according to claim 9, wherein pis
 1. 12. The process according to claim 9, wherein q is
 1. 13. Theprocess according to claim 9, wherein X is S or NH and R¹ and R² areboth H.
 14. The process according to claim 13, wherein the monomer offormula II is 2,2'-dithienylmethane.
 15. The process according to claim13, wherein the monomer of formula II is 2,2'-dipyrrylmethane.
 16. Theprocess according to claim 9, wherein the solvent contains anelectrolyte compound that is ionizable in the solvent to provide anionicdopant ions that dope the electrically conducting organic materialduring its formation on the anode.